1. Field of Invention
The invention relates to a gauge block used as a standard when measuring an accurate length dimension.
2. Description of Related Art
Gauge blocks have been employed as a standard when measuring an accurate length dimension. A gauge block is required to have excellent abrasion and corrosion resistance because it is the standard for the accurate measurement of a dimension. If the gauge block is worn or eroded, it cannot be useful as a standard any longer. In addition, ringing, in which a gauge block is employed so as to contact tightly with another gauge block, cannot be performed. Therefore, steel, ceramics, low thermal expansion glass and so forth have been utilized as materials of a gauge block.
A gauge block made of a metal such as steel does not have sufficient corrosion resistance. Thus, it is necessary to keep a steel gauge block in a completely anti-corrosive environment. This creates a disadvantage in that handling becomes extremely complicated. For example, anti-corrosive gloves must always be worn during handling. It has been attempted recently to improve the abrasion and corrosion resistances of metallic gauge blocks in order to solve the above disadvantages. However, the selection takes a long time, for example, to select materials for heating and so forth. This creates another disadvantage by increasing the production costs.
In particular, to improve the abrasion resistance of a steel gauge block, it has been necessary to heat and quench harden the steel gauge block to increase its hardness. The quench hardening causes a structural variation, however, which create the disadvantage of time-dependent changes in dimension. In addition, quench hardening increases the cost.
Some methods have been employed recently to reduce the time dependent changes in dimension. They include special heat treatments such as a subzero or temper treatment. They also include an artificial aging treatment and natural aging. However, sufficient results are not always achieved. In addition, the special treatment further increases the cost.
Publication JP 8-20201 (B) discloses a technology that forms a hard thin film over the reference surface of a gauge block. This technology is mainly directed to preventing the reference surface from being contaminated by forming a hard thin film with a rough surface. The formation of the roughness on the reference surface makes it impossible to perform ringing, in which a plurality of gauge blocks are employed by contacting one reference surface tightly with another. To perform ringing requires a reference surface that has high smoothness and no roughness.
An object of the present invention is to provide a gauge block, which has excellent abrasion and corrosion resistances without being affected by time dependent changes in dimension and which can be produced inexpensively.
The present invention is a gauge block, which includes a gauge block body and a diamond-like carbon film coated thereon.
In the present invention, the gauge block body may preferably include a raw steel material that is not hardened or a raw steel material having at least one reference surface which is quench hardened.
According to the present invention, the performance and reliability of the gauge block can be improved by coating the gauge block body with diamond-like carbon film (DLC film) that has excellent abrasion and corrosion resistance.
In a case where non-hardened raw steel material is employed as the gauge block body, a stable gauge block, usable for a long time can be obtained. This is due to the absence of time-dependent changes in dimension due to the structural variation that are caused when the material is quench hardened. In addition, quench hardening, special heat treatments (subzero and temper treatments), artificial aging treatment and natural aging are not required. Thus, the production cost and time can be reduced.
The gauge block body to be coated with DLC may also include ceramics or low heat-expansion glass. The ceramics are preferably ceramics mainly consisting of zirconia (zirconium oxide: ZrO2). The low heat-expansion glass may be a solid solution type as including 60-70 wt. % silicon dioxide, SiO2, as the main part, 15-25 wt. % aluminum oxide, Al2O3, and 1.5-5 wt. % of lithium oxide, LiO2.
The coating of the DLC film may be performed by a physical vapor deposition (PVD) method, preferably a multi-arc ion plating method that can form a super thin DLC film with a thickness of several nm or less with good controllability. The DLC film is to be formed amorphous where the surface is smooth and has a low coefficient of friction. Accordingly, by polishing the gauge block body so that the dimension between the reference surfaces become a desired value, finish polishing would not be required after the DLC film is formed.
Other features and advantages of the invention will be apparent from the following description of the preferred embodiments thereof.